English is one of the world's most important languages ___

问题描述:

English is one of the world's most important languages ___
a.as it is so widely used b.if it is used very wide
c.it is used until so widely d.for it is quite wide used
为什么选A?还有就是形容词,副词句中的用法在此句中

这里的as是表原因,还Because一样.
it is used 表被动.被使用,widely副词修饰动作.